Liquid crystal displays (LCDs) do not operate well at low temperatures. At temperatures of approximately -20 degrees C. and below, the LCD fluid becomes too viscous to respond to an applied electric potential within a specified time. Because it is the fluid in the LCD and not the remainder of the device that must be heated during low temperature operation, LCDs can be procured with integral heater elements. Although most LCD materials can be utilized in a static mode between temperatures of -20 to -40 degrees C., the application of heater power is necessary for operation of dynamic areas of the display at these low temperatures.
An integral heater element for an LCD generally comprises a thin film of transparent indium tin oxide (ITO) deposited on the LCD. By maintaining an electric potential connected to one edge of the ITO heater and switchably connecting the opposite side of the heater to ground, the LCD can be selectively heated during cold temperature operation. However, applying a potential across a uniform coating of ITO on the LCD results in a thermal gradient. Because the LCD is mounted in a support structure, the edges of the heated LCD can remain much cooler than the center of the display because the mounting structure acts as a heat sink. Thus, the center portion of the LCD can be over-heated while the edges remain too cold.
LCD heating systems also tend to consume a lot of power while requiring lengthy warm-up periods. Some cold weather LCD operating situations, such as a scramble of military aircraft on cold weather alert, require rapid LCD warm-up without excessive use of power. Thus, there is a need for an LCD heating system that reduces warm-up time, reduces power consumption, and provides a more uniform temperature gradient across the entire display during cold weather operation.